Ion implantation is an important process in semiconductor/microelectronic manufacturing. The ion implantation process is used in integrated circuit fabrication to introduce dopant impurities into semiconductor wafers. The desired dopant impurities are introduced into semiconductor wafers to form doped regions at a desired depth. The dopant impurities are selected to bond with the semiconductor wafer material to create electrical carriers and thereby alter the electrical conductivity of the semiconductor wafer material. The concentration of dopant impurities introduced determines the electrical conductivity of the doped region. Many impurity regions are necessarily created to form transistor structures, isolation structures and other electronic structures, which collectively function as a semiconductor device.
The dopant impurities are generally ions derived from a source dopant gas. An ion-source filament is used to ionize the dopant gas source into the various dopant ionic species. The ions produce a plasma environment within the ion chamber. The ions are subsequently extracted from the ion chamber in the form of a defined ion beam. The resultant ion beam is typically characterized by a beam current. Generally speaking, a higher beam current can allow more dopant ionic species to be available for implantation into a given workpeice, such as a wafer. In this manner, a higher implant dosage of the dopant ionic species can be achieved for a given flow rate of source dopant gas. The resultant ion beam may be transported through a mass analyzer/filter and then transported to the surface of a workpiece, such as a semiconductor wafer. The desired dopant ionic species of the beam penetrate the surface of the semiconductor wafer to form a doped region of a certain depth with desired electrical and/or physical properties.
Silicon implantation has been widely used in the semiconductor industry for a variety of material modification applications such as amorphization or photoresist modification. The increasing use of Si implant steps during device fabrication is requiring a need for an improved process for implantation of various Si ionic dopant species characterized by an increased beam current without compromising ion source life. The higher beam current may allow higher equipment throughput and significant productivity improvements. It should be understood that the terms “Si ions”, “Si ionic species”, “Si ionic dopant species” and “Si+ ions” will be used interchangeably throughout the specification.
Silicon tetrafluoride (SiF4) has been utilized as a dopant gas source for silicon ion implantation. However, SiF4 has various drawbacks. Of particular significance, SiF4 may be limited in its ability to ionize and generate the requisite amount of Si+ ions to establish the higher beam current being demanded by today's applications. Increasing the amount of Si+ ions that are generated from SiF4 typically requires increasing the energy inputted to the ion source, otherwise referred to in the industry as the operating arc voltage of the ion source. However, operating at increased energy levels can damage the ion source components, which may ultimately reduce the ability of the ion source to generate Si+ ions during operation. For example, as the walls of the arc chamber increase in temperature during a typical ion implant process, active fluorine that is released from SiF4 can more rapidly etch and erode the tungsten chamber walls, which can cause the cathode to be more susceptible to increased deposition of W-containing deposits. The W-containing deposits suppress the ion source's ability to generate the threshold number of electrons necessary to sustain the plasma and generate Si+ ions. Additionally, more active fluorine ions are available to propagate the so-called detrimental “halogen cycle” by which increased chemical erosion of the ion source chamber wall and other chamber components can occur. Accordingly, operating the ion source chamber at higher energy levels in an attempt to increase ionization of SiF4 has the potential for shorter ion-source life, thereby rendering this mode of operation undesirable.
Currently, there are no viable techniques for maintaining or increasing the beam current of Si+ ion without damaging the ion source chamber components. There remains an unmet need to develop compositions, systems and methods of use thereof to improve the beam current of the desired silicon ion species without compromising the ion source life.